Abstract
Studies of metal-salen complexes are of great interest due to their versatile nature and widespread applications. Metal-salens have also shown to have good photophysical properties and biological activity which has driven multiple studies on their ability to function as photosensitizers. The most commonly used metal-salen is N,N’-Bis(salicylidene)ethylenediamino nickel(II); Ni(II)-salen. In the present study, we assessed the ability of DFT to predict the ?max of a series of metal-salen complexes, and the effect of solvent on the accuracy of those predictions. The computational programs PC Spartan and Gaussian were used to carry out this study. Calculations were done in the gas-phase on PC Spartan, and with applied solvent in Gaussian. From the results in this study, it is clear that solvent plays a significant role in the accuracy of the of the ?max predictions for metal-salen complexes. The metal-salen complexes that were singlets at their lowest spin state were investigated for their ability to function as photosensitizers in the photoisomerization of stilbene. Using PC Spartan the singlet ground state, singlet excited state and triplet excited state were determined for both the substrate stilbene and metal-salen sensitizer. It was found that the T1 for the stilbene substrate was larger in energy than that of the nickel metal-salen sensitizer. It was also found that the R,R aluminum chloride metal-salen had a triplet excited state that was larger an energy than its corresponding singlet excited state. Ideally, for a photoisomerization to take place, the difference in energies for the triplet electronic state of the sensitizer should be larger than those for the substrate. Two more compounds, beta-Carotene and Lycopene, were analyzed as substrates for a photoisomerization reaction with metal-salens as the sensitizer. It was found that the triplet electronic states for these two compounds were much lower than that of stilbene, suggesting that the metal-salen complexes could function as good sensitizers for a photoisomerization reaction with beta-Carotene or Lycopene being the substrate.